MSN Search ... is ... Internet Explorer's default search engine. I would consider any dip in IE browser market share as a threat to MSN Search -- and one Microsoft shouldn't ignore.

It's a good point. By default, anyone powering up a new computer will use IE. Their web search will be MSN Search. The first web page they see every day will be MSN.com. This guarantees MSN a large customer base. If some computers come with another browser installed or enough people are motivated to install a new browser themselves, then that is a threat to MSN's revenue stream.

But I think Joe understates the importance to Microsoft of the continued dominance of IE. IE was created because Netscape was a threat to the Windows desktop. Networked applications running through a browser reduce the importance of the OS and desktop applications. Loss of IE market share threatens not just MSN but all of Microsoft.